When you open a mold design review, the first question is usually not cavity layout but mold base type. From the standard two-plate (A/B plate) base to three-plate, hot-runner, and stack molds, the choice drives plate thickness, guide-pin layout, ejector stroke, and even the size of the injection machine tie-bar spacing. In a typical two-plate base for a 200–500 g ABS part, the A plate might run 80–120 mm and the B plate 100–150 mm, with a 25–35 mm ejector plate package. Three-plate bases add a runner stripper plate, often 20–30 mm, to allow pin-point gating and automatic degating—critical when you need balanced filling across 4, 8, or 16 cavities. Hot-runner bases replace the runner plate with a manifold pocket, so you must reserve 40–60 mm for the manifold plus insulation, and keep plate flatness within 0.02–0.05 mm to avoid leakage at the nozzle tips.

In practice, 24 common structural layouts cover most jobs: side-gate two-plate, direct-gate, three-plate pin-point, hot-runner direct, hot-runner valve-gate, stack mold, and variations with slides, lifters, and secondary ejection. For a 16-cavity hot-runner base, a typical manifold has 4 drops per zone and needs 8–12 mm thermal expansion clearance at the nozzle seats. Guide pins should be at least 20–25 mm diameter for bases over 400×400 mm, and return pins must be long enough to protect the core before mold closing. If you use a stack mold, the center section often needs an additional 30–50 mm of daylight, and the ejection system must be synchronized on both parting lines. These details are what separate a mold that runs 500,000 cycles from one that flashes or sticks at 50,000.

For sourcing, don’t just order a catalog base and hope it fits. Check the steel grade—P20, 718H, or NAK80—and whether the plate has been pre-hardened to 28–34 HRC. Confirm the ejector hole pattern matches your ejector plate, and verify the locating ring diameter against your machine’s platen bore. If you’re building a hot-runner mold, ask for the manifold drawing and heater wattage before you cut the pocket. A 10 mm mistake in plate thickness can cost you a week of rework. For more mold sourcing and design references, visit MoldWorld at www.moldw.com.